Casey is a 2-4-0 American steam tender locomotive with a small, four-wheeled tender full of coal at the back, a big, tall smokestack, a small headlamp in a baseball cap-shaped casing, a tall steam dome with a whistle on top, and a small cowcatcher on his front. Its front has a vague shape of a face, with two headlights in place of eyes and a cylinder-shaped structure protruding forward functioning as its nose. The wheel pistons are often used as "arms", like when Casey has to climb up a difficult mountain.
Casey is a 2-4-0 American steam tender locomotive hauling the WDP Circus train, and he even has his own theme song. He appears frequently throughout the film and is shown to be somewhat sapient. For example, when the Ringmaster calls, "All aboard! All aboard!", his whistle can be heard calling, "All aboard! Let's go!"
As is the case with most of Disney's early cartoon vehicles, Casey has the ability to move more fluidly than real-life locomotives, and his boiler is often seen bending and twisting like rubber when in motion. In addition, Casey can twist and flex his metal body to express motion. He uses his steam cylinders like limbs, giving him the ability to shrug, point and make other gestures.
While the sound of the voice resembles that of one processed through a vocoder, it was actually done with a more primitive device, a Sonovox, which uses one or two small loudspeakers in contact with the throat, which allowed Wright to "speak" by modulating an artificially produced sound with her mouth.
In this live-action/animated tour of the Walt Disney Studio in 1941, a work-in-progress scene of Casey is used to demonstrate the creation of sound effects for animation as well as the vocoder device used to create his voice. This demonstration takes the form of an extended train journey, though it is hard to say whether this was truly a deleted scene from an early version of Dumbo or simply new animation created for the purposes of the demonstration.
In this scene, Casey was, in fact, pulling a passenger train to Cleveland, Ohio. At one point during the excursion, he gets into conflict with a steamboat over the right of way on a drawbridge that spans the river, before overcoming him and causing the drawbridge to close on and push down on the steamboat into the water. Later on, Casey encounters a streamlined train charging towards him and closing in fast, at which he desperately called for a nearby railroad switch lever to wake up and change the track, which it did. He thereafter crashes after an effort to jump the chasm left by a broken bridge in a storm.
Casey's design in this film differs from his prior appearance in Dumbo and thus features many changes. For starters, coupling rods were connected to his foremost driving axle. He also had a roof-mounted bell and was not as stubby. When he was hired for the circus train, he had a few changes: his coupling rods were extended and moved to his rear driving wheels, his bell was removed, and he became stubbier. This implies that he was overhauled after the accident and bought by a railroad based in Florida that served the southeastern United States.
In Kronk's New Groove, the sequel to The Emperor's New Groove, Kronk has a miniature model train set of Casey Junior in his new home, complete with scaled-down models of the carriages featured in Dumbo.
Casey Junior makes two cameo appearances in the Mickey Mouse TV shorts. In the episode Tokyo Go, he appears at the end of the episode as a miniature train piloted by Mickey Mouse as a children's attraction, in reference to Walt Disney's backyard Carolwood Pacific Railroad, complete with Walt's barn (a photo of Walt in the cab of Disneyland Railroad locomotive E. P. Ripley also appears in the scene). Casey also appears in the episode "New Shoes", with his namesake, Casey Jones, engineering, riding with Dumbo, Timothy, and the Crows.
Casey makes a cameo at the beginning of the 2016 live-action Jungle Book remake during the film's opening Disney logo (re-created using traditional animation instead of CGI, thus replacing the realistic train from the original version of the current logo), where he is seen as a silhouetted train crossing a trestle over a river behind an amusement park just right before the castle is shown. This is the same logo used for the 2019 remake of The Lion King; however, unlike in The Jungle Book, the logo does not back into a jungle and instead fades away. Coincidentally, both films are live-action remakes directed by Jon Favreau.
A non-anthropomorphic Casey Junior also appeared in the 2019 live-action remake of Dumbo.
Casey Junior appears in the video game Mickey's Racing Adventure as the train which brings the characters to their racing grounds. In the game, Casey is not anthropomorphic but maintains the same name and appearance it had in Dumbo.
Casey makes a brief cameo in Where's My Mickey?.
A Disneyland attraction named the Casey Jr. Circus Train is based on Casey, with an updated version running at Disneyland Paris. Casey Jr. Splash & Soak Station, a water play area themed around him, was added to the Magic Kingdom in 2012 in the Storybook Circus section of that park's new Fantasyland.
Casey is the second float in the Main Street Electrical Parade and its versions. He, driven by Goofy, pulls a drum with the parade logo, along with Mickey Mouse and Minnie Mouse. When the parade returned to Disneyland in 2017, he was made the lead float.
- Despite Casey being painted black in the original film, he has instead been painted a bright blue in most other material, including the theme parks and in the live-action remake.
- In the original movie, Casey's eyes have visible pupils only in two scenes: when the whistle calls "all aboard" and in the final scene, which is also the only time the train also has a mouth. (This latter depiction of Casey can also be seen in the early trailers for Dumbo, albeit without the decorations around his smokebox).
- The wagons that transport P.T. Flea's Circus in A Bug's Life are old boxes of Casey Jr. cookies.
- In the film, Casey does not appear to have an engineer in his cab, so it is unknown how he is able to move on his own in the first place unless he is a sentient being.
- When Casey climbs up the mountain, he chants, "I think I can," over and over again, and on the way down he chants repeatedly, "I thought I could." This is a direct reference to the classic children's book The Little Engine That Could, in which the titular anthropomorphic locomotive chants these same words. In addition, Casey's cab and firebox have their colors briefly inverted.
- The "Casey Junior" segment in Dumbo was possibly much longer during the film's production. Not counting the segment featuring Casey in The Reluctant Dragon, concept artwork showed a possible deleted scene where Casey stops to drink water near a waterfall.
- Casey's train, for some reason, seems to be constantly gaining and losing cars as he makes his journey; the only time he is ever seen with all of his cars intact is when he crosses a bridge before climbing up the mountain.
- The train Casey pulls in the film, from front to back, is made up of a yellow coach (carrying the clowns and other circus performers), a flatcar with a calliope organ and a various circus wagon, another flatcar (carrying two other various circus wagons), an orange stock car (carrying the elephants), a blue stock car (carrying animals like monkeys, horses, zebras, and camels), another flatcar (carrying the tent and its supports), a light blue stock car (carrying the giraffes [whose heads are clearly sticking through the roof]), one more flatcar (carrying two more wagons), a pink stock car (carrying predators like hyenas, apes, bears, lions, and tigers), a light green stock (carrying animals like ostriches, seals, hippos and kangaroos), a green coach (carrying the circus workmen), and a red caboose numbered 2 (carrying the ringmaster). Also, at the end of the film, the caboose is replaced with a silver coach reserved for Dumbo and Mrs. Jumbo.
- In Dumbo, Casey is a 2-4-0 steam locomotive, most likely to be of an American design, and numbered "8" on the Illinois Central Railroad and "1" on his own railroad, but in the 2019 live-action film Dumbo, Casey appears as a 4-4-0 American steam locomotive, and numbered "41".
- The number 41 is the reference to the year of the original animated version of "Dumbo" which was released in 1941.
- In the live-action remake, it also has an engineer and fireman with it, and it's a wood-burning steam locomotive. Its tender is lettered Medici Brothers' Circus but later re-lettered to Medici Family Circus. It is also a non-speaking character and a non-anthropomorphic train, but it does have an inanimate face.
- The color schemes that Casey is wearing in the live-action remake is the same one that Casey wears at Disney parks, and similar to what locomotive No. 2, that Casey Jones pilots, is wearing in The Brave Engineer.
- Casey strongly resembles a locomotive that was built by Baldwin Locomotive Works in 1900 for the Old Sydney Colliery Company. This locomotive (numbered 25) worked at the Sydney, Nota-Scotia colliery until the early 1960s. It is currently on display at Delson, Quebec, Canada today. He also bears a considerable amount of resemblance to the Virginia & Truckee's #21 locomotive "J.W. Bowker", and even more so to the Denver & Rio Grande #1 "Montezuma" (despite the latter being 3-foot narrow gauge, it had a 4-wheel tender much like Casey's). As a matter of fact, animator Ward Kimball owned an 1881 Baldwin Mogul 2-6-0 steam locomotive, which he ran on the Grizzly Flats Railroad. Casey is based on that particular locomotive.
- In the live-action remake, it strongly resembles a Pennsylvania Railroad Class D6 they were built by the PRR's Altoona Works between 1881–1883 for the Pennsylvania Railroad. But except with a diamond stack, a shorter 6 wheeled tender, and no running board for Casey.
- Casey's sound was reused for the dishes from The Sword in the Stone, during which Sir Ector pushes the dishes aside violently.